The invention relates generally to the field of magnetic bubble technology (MBT) and, more particularly, to means for propagating or transmitting magnetic bubbles, especially in recirculating closed loops.
Briefly, MBT involves the creation and propagation of magnetic bubbles in specially prepared magnetic materials. The word "bubble", used through this text, is intended to encompass any single-walled magnetic domain, defined as a domain having an outer boundary which closes on itself. The application of a static, uniform magnetic bias field orthogonal to a sheet of magnetic material having suitable uniaxial anisotropy causes the normally random serpentine pattern of magnetic domains to shrink into short cylindrical configurations or bubbles whose common polarity is opposite that of the bias field. The bubbles repell each other and can be moved or propagated by a magnetic field in the plane of the sheet.
Many schemes exist for propagating bubbles along predetermined channels. These techniques can be classed generally as conductor-accessed and field-accessed. In conductor-accessed propagation systems, loops of electrical conductors are disposed in series over the magnetic sheet. A propagation system has been proposed using a "serpentine" conductor crisscrossing a ferromagnetic rail defining stable complementary bubble positions. In field-accessed propagation systems electrical conductors are not disposed on the magnetic sheet for propagation; instead, an overlay pattern of ferromagnetic elements establishes a bubble propagation channel in which a sequence of attracting poles is caused to be formed in the presence of a continuous, uniformly rotating magnetic drive field in the plane of the sheet. A major distinction in function between conductor-accessed and field-accessed circuits is that several conductor-accessed circuits can be disposed on the same sheet or "bubble chip" and operated completely separately and exclusively from each other, while field-accessed circuits on the same chip all operate at the same time under the control of an ubiquitous, uniformly rotating, common drive field.
One attempt at providing field-accessed circuit selection in the prior art is shown in U.S. Pat. No. 3,543,252 to Perneski illustrating several variations on the familiar T-bar circuit driven by different permutations of pulsed orthogonal drive fields.
MBT can be used in data processing because magnetic bubbles can be propagated through channels, whether field-accessed or conductor-accessed at a precisely determined rate so that uniform data streams of bubbles are possible in which the presence or absence of a bubble at a particular position within the stream indicates a binary "1" or "0". Because of its potential for low cost, low power consumption and extremely high bit density, MBT is under active consideration for use in large scale relatively low speeds memories. One of the prime design elements of many memory systems utilizing field-accessed magnetic bubbles is the provision of a serial closed loop bubble path which can be used as a recirculating "shift registor". Many memory arrangements of this type employ a plurality of "minor" loops selectively interconnectible with a "major" loop such that bubbles can be transferred between the major and minor loops on command. The ability to propagate bubbles in one recirculating loop without operating other loops on the same chips has in the past been confined to systems employing conductor-accessed circuits.
Another consideration to which this application is directed is the desirability of providing a segmented continuous overlay rather than discrete spaced element such as those used in chevron and T-bar circuits. U.S. Pat. No. 3,518,643 to Perneski illustrates zigzag and crenallated forms of continuous overlay patterns based on right angles, driven by a pulsed orthogonal coil arrangement.
Other forms of pulsed field-driven circuit overlays are shown U.S. Pat. No. 3,934,236, entitled "Pulsed Field-accessed Bubble Propagation Circuits" by the same inventors as this application, filed on the same day as this application, assigned to the assignee of this application, and incorporated by reference herein.